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Material and surface characterization

Please find information, research projects and publications regarding material and surface characterization in this section.

General characterization

Projects

  • Mechanical joining of dissimilar materials by shear clinching processes without pre-punching (shear clinching), Institute of Manufacturing Technology (LFT) Friedrich-Alexander-Universität Erlangen-Nürnberg, Germany:

    An efficient use of energy and raw materials requires the design of components based on lightweight structures. One possible approach for this is the use of different metallic materials or metals and polymers in composite construction. Thus, the specific properties in terms of functional performance, operational safety and resource consumption can be optimized by suitable combinations of materials. Therefore, it is essential to establish a reliable component connection by means of adequate joining technologies. Established joining methods for single material connections are only limited applicable to this due to the different behavior of the joining partners. Great potential for joining different materials offers shear clinching, which is investigated in this project. The joining process is fundamentally realized by plastic deformation of the materials without additional aids. The shear clinching process is based on a clinching process, where the connection results from a material flow of the upper joining partner behind the pre-cut bottom partner. In contrast to this method the mechanical joining is performed without pre-cut in the investigated shear clinching process. This leads to a reduction of steps in the process chain.

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Fatigue strength

Projects

  • Fine Machining of Tool Surfaces, Institute of Manufacturing Technology (LFT) Friedrich-Alexander-Universität Erlangen-Nürnberg, Germany:


    Due to the high stresses in cold forging high speed steels (HSS) and cemented carbides (CC) are often used as tool materials. In many cases complex tool geometries are hard machined by electrical discharge machining (EDM). For improvement of surface properties the white layer caused by EDM is usually removed by cost intensive polishing. For reduction of polishing effort as well as for improvement of ED machined surfaces different post machining methods after EDM are available. In this project the fatigue behavior of tools made of HSS and CC manufactured by the process chain “EDM - post machining - polishing” is investigated. Aim of the project is to derive requirements and recommendations from the gained correlations between tool manufacturing, surface properties and fatigue behavior for an optimized tool production.
  • Experimental and analytical studies on the Ti-6Al-4V cold expanded fastener hole,  Northwestern Polytechnical University, China:

    The distribution of crack initiation life was determined by metallographic fracture data. Based on the crack growth formula,the equivalent initial flaw size which characterized the initial fatigue qualify was obtained by optimizing the reference crack size and the upper limit of equivalent initial flaw size. The rated equivalent initial flaw size was then determined. Referring to a designated economic repair size,the economic repair life with the reliability of 95% was obtained using the theory of probabilistic fracture mechanics.
  • Development of technology for improving die life in bolt forging process using high-strength wire rod (2013-2016), Korea
  • Cold forging tool fatigue behaviour, the low cycle fatigue (LCF) behaviour of a Cr-Mo-V matrix-type high-speed steel (matrix-type HSS), The Institute of Forming Technology & Equipment (IFTE) of School of Materials Science and Engineering (SMSE) at Shanghai Jiao Tong University (SJTU), China:

    Strain-controlled fatigue tests were conducted under strain-controlled cyclic loading conditions with different axial strain amplitude levels at room temperature. The cyclic strain-stress relationship and the strain-life relationship were obtained.The fatigue damage process through the crack initiation and propagation was explained through observing the features of the fractures. Based on the core of evolutionary structural optimization(ESO) and considered the bulk metal forming features, a method-topology optimization method is proposed and adopted for preform design of bulk metal forming.
  • Load oriented component properties for lightweight and high performance applications through efficient, optimized cold forging processes, Institute of Manufacturing Technology (LFT) Friedrich-Alexander-Universität Erlangen-Nürnberg, Germany:

    The optimization of components for lightweight and high performance applications by using the advantages of cold forging, e.g. strain hardening and orientation of fibers was aim of the project. Especially the influence of the cold forging process on the fatigue strength of components was analyzed. For the investigations fatigue tests have been conceptually designed and executed to determine the correlations between properties and strength of the components. Furthermore, the properties of the components, for example the distribution of true strain and residual stresses, have been calculated using numerical simulations. For small numbers of load cycles the hardness is the important factor in terms of fatigue strength, for the endurance limit the surface properties and residual stresses are important.
  • Dynamic strength of tool steels, Institute of Manufacturing Technology (LFT) Friedrich-Alexander-Universität Erlangen-Nürnberg, Germany:

    Study, funded by the German Cold Forging Group (GCFG) In cold forging the tools have to resist highest cyclic loads because of the high flow stress of the workpiece material. Due to the cyclic loading of the tool during the forging process a main failure cause are fatigue cracks. According to the SVL-concept a tool failure due to fatigue must be expected if the maximum process load is higher than the fatigue strength of the tool material. Thus, fatigue parameters of the used tools steels are very important for the tool- and the process-layout. In the context of the study, Woehler curves for the powder-metallurgical steels CPM1V with a hardness of 59 HRC and ASP2013 with a hardness of 60 HRC have been identified. The experiments were carried out with an electromechanical resonance pulsator using a customized tension/compression specimen. The load amplitude of the Woehler experiments was up to 1,600 N/mm² and the level of the mean stress was varied between -640 and 0 N/mm². Applying a compressive mean stress is comparable to the case of a prestressed die. The created Woehler curves are covering the range from low cycle fatigue with 3·103 load cycles up to high cycle fatigue with 106 load cycles. Hence, the results of the study are a good basis for the layout of forging tools where a lifetime of at least 105 load cycles is expected in many cases.

Publications

  • Zhang Y, Hu CL, Zhao Z, et al. Low cycle fatigue behaviour of a Cr-Mo-V matrix-type high-speed steel used for cold forging. Materials and Design, 2013, 44: 612-62
  • Andreas, K.; Merklein, M.; Engel, U.: Fatigue Behavior of Cemented Carbide Based Forming Tools. In: Proceedings of the 18th Plansee Seminar, 2013, Reutte, in print        

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Tribology

Projects

  • Bulk metal forming at elevated temperatures – Extrusion of steel between room temperature and 500°C, Institute for Metal Forming Technology (IFU) University of Stuttgart / Germany – Status report July 2013:

    Metal forming of coated aluminum and steel raw material within temperature range below 500 °C provides numerous advantages compared to established cold and warm forming processes under economic conditions. Such temperature range below blue brittleness between 300 °C and 500 °C for e.g. steel alloys, which is characterised by a high ductility and low yield stress, in this project is of particular interest. In addition to an increase of formability forming at elevated temperatures a notice­able decrease of tool load and an increase of tool life time respectively is observed. To gain a deeper understanding of forming processes at elevated temperatures this study is based on the three work packages: tribology, technological material properties and process investigations. End of work might be expected end of year 2013.
  • Manufacture of a shaft-hub connection by lateral extrusion, Institute for Metal Forming Technology (IFU) University of Stuttgart / Germany – Status report July 2013:

    Nowadays the design of positive locking shaft-hub connections often is limited by manufacturing tolerances due to mechanical machining of shaft and hub. Especially novel contours based on complex cycloids, which demonstrate a high potential in numerical analysis, cannot show its potential in practice due to manufacturing tolerances and assembling clearance. Following new solutions of this study, the final machining of shaft geometry is no longer necessary by joining a shaft-hub connection by lateral extrusion. One part of this investigation embrace a hub made of tempered 42CrMo4 and a shaft made of 16MnCrS5 (GKZ annealed) are joined by lateral extrusion of shaft. Beside tribology conditions or hub's internal profile type the radial preload of the hub is investigated considering high degree filling the cavity of hub along its length. First results using a polygonal hub profile (P3G) show that high friction leads to an increase of radial material flow and thus to a higher degree of filling of cavity. Unfortunately, the increase of degree of cavity filling cause higher radial deformation and higher residual stresses of hub. The properties of the manufactured joints are checked by static and dynamic investigations.

  • Environmentally friendly process chains in cold forging by abdication of zinc phosphate conversion layers, Institute for Production Engineering and Forming Machines (PtU) Technical University of Darmstadt, Germany:

    Cold forging processes provide a high dimensional accuracy and a good material utilization. Due to high tribological loads, which occur during forming, complex separation and lubrication layers are used to prevent wear and failure of expensive forming tools. Hence, zinc phosphate coatings as separation layers and soap as a lubricant are used for the forging of steel, though the application and use of zinc phosphate coatings come along with several environmentally drawbacks. Objective of this research project is to gather basic knowledge for the zinc phosphate-free, multistage cold forging of billets. Within this project new single layer lubricants are developed and used for cold bulk metal forming of steel. Therefore, the functionality of zinc phosphate free lubricants will be investigated with respect to the part’s surface structure. The use of fast applicable single layer lubricants permits innovative process sequences. Furthermore, an inline-surface treatment interlinked with a multistage forming process of billets will be realized within this project. In combination with a more environmentally benign manufacturing, shorter treatment times, lower buffer volumes and a higher grade of flexibility will be achieved. (Contact: Dipl.-Ing. Sebastian Zang)

  • Thermal-tribological analysis and optimization, Institute for Production Engineering and Forming Machines (PtU) Technical University of Darmstadt , Germany:

    Having high forming rates in cold forging, a high amount of energy is converted into heat and the tool temperature rises. However, a constant tool temperature can only be achieved after numerous strokes. In order to investigate the thermal tribological conditions and the interactions, a project of three industrial companies and the PtU aims to develop a computer-aided process design for a thermal-tribological analysis of cold forging processes. Experiments on the Sliding Compression Test of the PtU are necessary to gain the knowledge to develop the model of the friction behavior. Therefore, the heating and cooling equipment of the Sliding Compression Test was optimized. Now, nearly unlimited specimen temperatures and tool temperatures up to 400°C are possible. Also, a software tool to simulate the stationary temperature was developed and integrated sensors in the tools of production processes measure the occurring temperatures. (Contact: Dipl.-Ing. Christoph Müller)

  • Tribology of stainless steels, Institute for Production Engineering and Forming Machines (PtU) Technical University of Darmstadt, Germany:

    Stainless steel has an increasing importance for cold forging. However, there are high demands on the tool and the tribological system. Especially the lubricant needs further investigation and, therefore, in a first step the tribological loads must be defined. Thus, eight different cold forging processes have been simulated. It could be shown that the sliding distance, the surface enlargement and the relative velocity in comparison to the cold forging of low alloy steel do not change. Though, the contact normal stresses and the temperature tremendously rise up. In a second step, Sliding Compression Tests have been conducted with common tribological systems as well as new environmentally friendly single bath systems. The results show that some environmentally lubricants are suitable to bear the severe loads. However, there is a high impact of the occurring temperature on the adhesion. Accordingly, further investigations should regard the temperature during the cold forging of stainless steel in detail. (Contact: Dipl.-Ing. Christoph Müller)

  • Constitutive friction law for the description and optimization of tailored surfaces, Institute of Manufacturing Technology (LFT) Friedrich-Alexander-Universität Erlangen-Nürnberg, Germany:

    Subproject C1, Collaborative Research Centre SFB/TR73 (www.tr-73.de) The aim of the project, jointly processed by the Chair of Applied Mechanics (LTM) and the LFT, is to investigate and to enhance the tribological conditions within sheet-bulk metal forming (SBMF). Further the constitutive friction law for this new class of forming processes, developed by the LTM has to be improved. This friction law has to be validated with experimental investigations at the LFT. Having shown in the first phase of the project that tailored surfaces are able to improve the material flow in SBMF, the aim of the second phase is to determine the fields of applications in different forming process and to understand mechanisms for the development of a targeted design process for tailored surfaces. Also new lubrication systems are going to be qualified for the use within SBMF.

  • Reduction of friction in EHD-contacts by microstructured surfaces of components – design, layout and manufacturing by forming, Institute of Manufacturing Technology (LFT) Friedrich-Alexander-Universität Erlangen-Nürnberg, Germany:

    Subproject within the Priority Program 1551 “Resource efficient design elements” In highly loaded revolving sliding contacts, like for cam tappet matchings, friction in the contact zone of components can be reduced by specifically applied, well-defined microstructures. Likewise, the wear behavior of such microstructured surfaces determines the durability of components. Within the scope of this project a simulation based method will be developed in collaboration with a partner institute in Erlangen that allows the design of microstructures specifically adapted for the individual tribological load collective. A focus of the LFT-part is the elaboration of the technological basis for a repeatable production of components with microstructured surfaces by a combined extrusion micro coining process coping with the demands of large-lot production. Due to its filigree geometries accuracy of manufacturing of the micro coining punch by micro electrical discharge machining plays a significant role. For an overall view of the product life cycle the characterization of microstructured surfaces is of vital importance as a junction between design and manufacturing of the components as well as for the analysis of wear behavior in operation.

  • MARS - Self lubricating materials for automotive industry, Italy:

    The project that involves 8 industrial partners, 2 universities and 1 research centre is starting in 2011 (duration of 3 years). The objective of the project is the development of new lubricants and new coatings based on nano-technologies to reduce friction and wear in extruded components for automation industries.

  • Friction measurement by the tip test for cold forging, Korea

Publications

  • Groche, P.; Müller, C.; Stahlmann, J.; Zang, S.: Mechanical Conditions in Bulk Metal Forming Tribometers - Part One. Tribology International 62, S. 223 - 231, 2013.                                                   
  • Hanisch, T.; Filzek, J.; Müller, C.: Tribological Characterization of Industrial Cold Forging Processes by Laboratory Testing. Tribologie + Schmierungstechnik 59, S. 36–40, 2013.                                                   
  • Andreas, K.; Merklein, M.; Engel, U.: Werkzeugherstellung in der Kaltmassivumformung - Einfluss der Werkzeugoberfläche auf die tribologischen Bedingungen. wt Werkstattstechnik online, 10(2012), 672-677                                                   
  • Schrader, T.; Weschta, M.; Engel, U.; Tremmel, S.; Merklein, M.; Wartzack, S.: Microstructured surfaces in highly loaded EHD-contacts – manufacturing and tribological performance. In: Bouzakis, K.-D.; Bobzin, K.; Denkena, B.; Merklein, M. (Edt.): Proc. 10th International Conference THE "A" Coatings in Manufacturing Engineering, 2013, Aachen: Shaker Verlag, 99-109                                                   
  • Schrader, T.; Engel, U.; Geiger, M.; Merklein, M.: Mehrlagenbeschichtungen für den beanspruchungsgerechten Einsatz bei Kaltmassivumformwerkzeugen. In: Faulstich, M.; Geiger, M.; Kukla, H.; Wolf, G. (Edt.): Moderne Beschichtungen zum Verschleißschutz von Werkzeugen, 2012, Sulzbach-Rosenberg: DORNER PrintConcept, 181-208                                                   
  • K.H. Jung, Y.T. Im, Determination of a dimensionless equation for shear friction factor in cold forging, Journal of Tribology - Transactions of the ASME, Vol. 135, pp.031102-1-031102-9, 2013. 

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Hardness

Projects 


Publications

  • She DS, Yue W, Fu ZQ, et al. The effect of nitriding temperature on hardness and microstructure of die steel pre-treated by ultrasonic cold forging technology. Materials & Design, 2013, 49: 392–399.                   
  • Wu XX, San XY, Liang XG, et al. Effect of stacking fault energy on mechanical behavior of cold-forging Cu and Cu alloys. Materials & Design, 2013, 47: 372–376.                                                   
  • Bruder, E., Görtan, M.O., Müller, C.: Impact of severe pre-straining via different routes on the age hardening behavior of Al-Mg-Si alloys. Proceedings of International Conference on Strength of Materials (ICSMA 16), Bangalore, India, 2012.                                                   

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Residual stresses

Projects


Publications

  • Andreas, K.; Merklein, M.; Engel, U.: Influence of Combined Hard and Fine Machining on the Surface Properties of Cemented Carbides. Tribology in Industry, 34(2012)3, 119-127                                                   

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